1. Field of the Invention
This invention relates to a coupling device for joining together adjacent ends of two tubular components, such as two pipe ends.
2. Present State of the Art
Coupling devices are used to join together adjacent ends of tubular components, such as pipes, and must provide (a) a reliable securement together of the adjacent ends via the coupling device so as to resist separation and (b) a sealed joint to withstand leakage under pressure.
In addition to joining together two adjacent pipe ends, coupling devices can be used to join together other types of tubular components e.g. to connect an inlet or outlet pipe to a tubular fitting on a housing.
However, the present invention has been developed primarily in connection with the coupling together of large bore pipes of the type used by the gas and water supply industries. Pipes of this type are usually made of polyethylene, and large bore yellow gas pipes will be a familiar sight to motorists negotiating roadworks.
The commonly used method to connect together successive lengths of this type of pipe and/or of pipes to pipe fittings, involve heating of adjacent ends to partly melt the joining portions, pressing the joining portions so that they fuse together, and allowing the portions to cool and set as a unitary product. Electro-fusion may be used, thereby pipe fittings incorporate wound electrical wire coil resisters embedded in the socket, to provide a heating element used to fuse together pipe/fitting joints. In both types of permanent fusing together (butt and electro-fusion), electrical power is always required.
When electrical power is used, the need to achieve exacting operating and temperature conditions necessary to obtain reliable joints can only be provided by bulky, complex and expensive equipment. Furthermore, skilled operatives are needed, but even then it is difficult, if not impossible, to test the resulting joint integrity in situ, prior to commissioning.
Evidently, the quality and reliability of fused-together joints depends upon (1) operator skill, (2) quality of the materials used to make the joining components and (3) design tolerances in the manufacture of the joining components. It is also difficult to join together pipes of different materials of specifications. Imperfect standards in any single one of these three criteria can result in unacceptable joints, both from the point of view of leakage, and also for resistance to mechanical separation of the joint under load.
Furthermore, joints of this type are necessarily permanent, and therefore can only be un-made by cutting through the joined-together components (often requiring extensive groundworks to complete), and obviously this is not an easily releasable, and subsequently re-makable type of coupling. Also, cannot be assembled without completing the joint, which makes trial lay-outs difficult.